Twitter said Thursday that its chief operating officer, Ali Rowghani, has resigned from his executive role with the microblogging company, which has struggled to win over more users.

The social media company did not give a reason for the shake-up, saying in a Securities and Exchange Commission filing that Rowghani had resigned effective Thursday and "will continue to be a Twitter employee and act as a strategic advisor to the CEO." Rowghani confirmed the departure with a Tweet. "Goodbye Twitter," it read. "It's been an amazing ride, and I will cherish the memories."

Twitter went public last November, but its stock price has stumbled as the company has faced difficulty picking up users -- an area that was reportedly among Rowghani's responsibilities.

Despite its big profile in the media and among celebrities, Twitter has struggled to catch on with the broader public.

For one, the number of monthly active users is only barely growing. In late April, the company's first quarter filings showed the number of monthly active users increased just under 6 percent over the previous three months, to a total of 255 million users. 

But that monthly active user figure doesn't address a major issue related to the company's struggle growth: The number of people who try the service, and then abandon it.

Twitter has been secretive about the number of people who register for an account, data that would shed light on exactly what's going on among users. But an outside estimate by the Twitter-watchers at Twopcharts puts the total number of existing accounts at around 1 billion. If only around 250 million of those are monthly active users, that means there are roughly 750 million accounts lying dormant. That's three out of four accounts.

There are reasons new users might not take to the platform. For people just starting out, it's not always clear which other users to follow. And if there's no one following you, sending out Tweets as a new user can feel like shouting at an empty room. By contrast, new users of Facebook--which has many more active users than Twitter-- may find it easier to quickly link up with friends and see news through a feed curated by the social network.

A December analysis of the platform by Jon Bruner at O'Reilly found that the median Twitter account has only one follower. Even among the smaller subset of users that had posted publicly within the previous 30 days, Bruner found that the median account had just 51 followers. In fact, having 1,000 followers puts a user at the 96th percentile of that group.

In recent months, Twitter has tried to find way to entice new users to stay and re-engage older users -- including a profile overhaul that rolled out across the platform. But so far, the market remains skeptical despite the company's significant revenues. Sales in the first quarter were $250 million, more than double where they were a year ago.

Still, Wall Street is reflecting the general skepticism about Twitter's prospects. While its stock price is up from the initial public offering price of $26 per share, its current $37.17 share price is a huge fall from the $73.31 the company was trading at in late December.

Twitter stock price since IPO (Source: Google)

The stock took an additional beating in May after the lockup period expired, allowing insiders and early investors to sell off some of their stake in the company. A number of executives sold off some of their shares, with the departing Rowghani dropping the largest chunk: 300,000 shares for a profit of around $9.9 million.

A Twitter spokesperson did not immediately return a request for comment. Rowghani, who joined Twitter in 2010 after working at Pixar, could not be immediately reached for comment. 

On Thurdsay, a number of Twitter employees, including chief executive Dick Costolo, responded to Rowghani's tweet, thanking him for his service to the company.

@ROWGHANI Thank you for being an incredible executive & partner. Twitter could not have succeeded without you.

— dick costolo (@dickc) June 12, 2014

The company does not plan to hire a replacement for the COO role, according to the SEC filing. Instead, the company said, "all of Mr. Rowghani’s operating responsibilities will be assumed by other members of the Twitter management team."

The microblogging platform's executive team has seen a fair amount of turmoil in the company's short lifetime. In 2008, then chief executive and co-founder Jack Dorsey was replaced by fellow co-founder Evan Williams. Williams himself stepped down in 2010, after which then-COO Costolo stepped into the role.